Best ND kit to start with?

All of those were taken with Hoya and B + W screw in filters with a 10-20mm f/4 lens, which has a 77mm thread. Unfortunately I had some expected vignetting problems with that particular lens and a filter holder, but really I prefer screw in filters overall to avoid that frustrating moment while shooting a seascape when drops of water somehow find their way into that narrow space between filter and lens :).